FX-Pressure Mod works just like the Pressure Mod section on the main synth parameters page, but instead of modulating synthesis parameters, it uses aftertouch data to modulate key effects parameters. (We'll refer to "pressure mod" as aftertouch, as that's the accepted terminology these days.)
Unlike the Pressure Mod section on the main page, FX Pressure-Mod is strictly mono, even if you're using a controller with poly aftertouch. Unlike the per-voice synthesis parameters modded by Pressure Mod (for example, each synth voice has its own filter cutoff frequency that can be individually controlled), the effects don't have multiples of each parameter, thus aftertouch must be monophonic. If you're using a controller that's transmits poly AT, the controller signals will be averaged to determine the control value.
Just to be 100% clear, the FX-Pressure Mod section functions totally independently of the Pressure Mod section on the main synth parameters page.
